Look, the main point about the Squeegee dero's is their Ninja-like ability to seize your windscreen before you realise whats happening, they are highly specialised and non-transferrable skills. Maybe he could use my car as practice for that? Expand his client list through surprise and shock tactics.
Depends on the quality of the work and how old the kids are. I'd say for under 10s they won't be able to clean the top of the car but the fact that they are actually taking the initiative to make some money, I'd give them $5 each. Over 10s or taller kiddos $5 for a basic job, $10 if they look like they are taking pride in their work.